The microbiome - an underestimated organ

The colonization with microorganisms begins during birth through exposure with bacteria from the mother's birth canal. (Photo: Pixabay.com)

The microbiome refers to the totality of all foreign genes that are found in the form of microorganisms in and on our body. Its composition varies from person to person and reveals a lot about our personality. What's more, it has our life in its hands.

In our organism, there are more microorganisms than human cells. For this reason, non-human genes are also numerically superior in our body. Among others, genes encode for proteins and enzymes, which in turn produce certain substances. No wonder, then, that every third metabolite in our blood is not human but of microbial origin. To believe that this is pure coincidence seems even crazier than the idea that our microbiota - the totality of all microorganisms - acts as an independent organ to sustain our health.

During the development phase, human beings are germ-free. The colonization with microorganisms begins during birth through exposure with bacteria from the mother's birth canal. Weeks after the birth, the baby's oral and intestinal flora is still similar to the vaginal flora of his mother. On the other hand, for children born by caesarean section, colonization takes place predominantly through contact with skin bacteria. A difference that could affect not only current but also adult health. Caesarean babies are at higher risk of suffering from allergies, asthma and other autoimmune diseases later in life. This is not proof of a connection with the type of first colonization, but it cannot be excluded that a connection may exist. In some places, caesarean babies are rubbed with a swab that has been previously placed in the mother's vagina to imitate the natural process.

An aura of bacteria

Over time, the entire skin, all mucous membranes and all body cavities are colonized by microorganisms. Something we share generously with our neighbors. For example, on our skin, the largest organ of our body, there is an ongoing exchange between "local" bacteria and bacteria from the environment. When touching, for example, or when kissing, millions of bacteria are exchanged. Even in the passive state, a human should deliver one million microorganisms per hour into the environment via the breath, falling dead skin cells and evaporated sweat. It is therefore not surprising that people who live closely together have a microbiome similar to that of other people. You could also say that the microbiome is inherited, which means that about 40% of the microorganisms belong to the basic equipment, so to speak. The remainder is determined by diet, lifestyle and predisposition, so that each person has his or her own individual microbiome. This could one day even play a role in forensics: If neither fingerprints nor DNA of the offender were to be found, his own bacteria could convict him instead.

• Microbe: smallest living organism• Microbiota: totality of all microorganisms in the human body• Microbiome: totality of all microbial genes in the human body• Flora: totality of microorganisms in or on a specific organ, eg. skin flora, oral flora, vaginal flora, intestinal flora• Probiotics: Bacteria or fungi that multiply in the intestine and confer a health benefit, eg. Lactobacilli, bifidobacteria, enterococci and yeasts• Prebiotics: Undigestible food components that can only be broken down by certain beneficial bacteria and thereby support their reproduction

Part of the digestion

Research on the microbiome is still at an early stage, but it is constantly bringing new findings to light. For scientists, the microbiome is a kind of super organ that interacts with many bodily functions. Perhaps the most obvious is its importance for digestion. Microorganisms can utilize components of the diet that would otherwise be indigestible. In this way they contribute to the production of energy as well as vital nutrients and vitamins. Vitamin B12, for example, can only be produced in sufficient quantity by a healthy intestinal flora. A sufficient vitamin B12- level is therefore less dependent on the diet than on the condition of the intestinal flora. Vitamin B12 is needed above all for the formation of red blood cells as well as for an optimal function of the nerve cells. Thanks to the microbes in the intestine, simple sugars and short-chain fatty acids are produced during the digestion of food from indigestible, complex carbohydrates. They alone cover 5 to 10% of the human energy requirement, whereas this can reach up to 70% for cows.

It is estimated that there are over 1000 different types of bacteria in the gut of an adult. (Photo: Pixabay.com)

Strengthening the immune system

It is estimated that there are over 1000 different types of bacteria in the gut of an adult. The greater the diversity, the better. In order not to lose one's mind at the large number of bacteria, these can be broadly speaking divided into "good" and "bad". The bad ones include, for example, colic or putrefactive bacteria. As long as their proportion is less than 15%, they are kept in check by the good bacteria. Lactobacilli and bifidobacteria are natural antagonists of the coli bacteria and keep the intestinal environment in balance. The dense bacterial film on the intestinal mucosa protects against infections from harmful bacteria, viruses, parasites and fungi. Interestingly, the bacteria of the microbiome are not controlled by the immune system, but tolerated. Indeed, the immune system depends on them to fend off harmful germs. But behind the scenes much more happens: One of the most important tasks of the intestinal flora is the training of the immune system. There is a constant exchange between intestinal flora and cells of the immune system. The processes are very complex. To put things simply, one could perhaps say that the intestinal flora teaches the immune system an appropriate behavior. Indeed, the line between under- and overreaction is narrow. Disorders of the intestinal flora can lead to faulty communication with the immune system and thus trigger autoimmune diseases and chronic inflammation.

Border control

The intestinal flora nourishes and cares for the intestinal mucosa and keeps it healthy so that it can fulfill its tasks. In addition to the absorption of nutrients, the intestinal mucosa has, above all, one function: to protect the organism from harmful environmental substances that reach the gastrointestinal tract through the food ingested. Close connections between the cells of the intestinal mucosa, so-called "tight junctions", ensure that substances do not slip through freely and enter the bloodstream. Should these sealing structures suffer damage, the intestine becomes permeable to toxic substances such as toxins, fungi, pathogens and incompletely digested food components. This in turn can trigger chronic inflammation and autoimmune diseases. This is also called "holey gut" or "leaky gut syndrome". For some time, certain pesticides from the food industry have also been suspected of causing such damage. In addition, there are bacteria whose metabolites contribute to the destruction of the seal. Cholera bacteria are an extreme example that cannot be ignored when causing severe diarrhea, unlike other bacteria whose mode of action is a bit more subtle. An intact intestinal flora could protect the barrier function from negative bacteria and influences.

The intestinal-brain axis

The small microbes in our intestines even affect our psychological well-being by communicating with the brain via the bloodstream and the nervous system. Depending on the composition of the intestinal flora, the microbiome can produce a variety of biologically active substances, including messengers such as GABA, dopamine, serotonin, norepinephrine and acetylcholine - the same neurotransmitters that control our feelings and actions in the brain. Animal experiments have already made it possible to establish a number of relationships. The studies were carried out either with axenic mice, which are kept sterile and have no intestinal flora. Or with animals whose intestinal flora has been deliberately manipulated, for example with the help of antibiotics, which can have a serious influence on the intestinal flora. In the case of a disturbed intestinal flora, one also speaks of dysbiosis, in which arises a different, non-health promoting ratio of the different bacterial species with each other. This means that less health promoting and more harmful substances are formed. Animal experiments have shown that mice without or with an artificially disturbed intestinal flora actually behave differently. They are less willing to learn and active, anxious and depressed, show increased stress reactions or autistic features. By transferring the intestinal flora of healthy mice, these effects were partially reversible. Of course, although these data can not be transferred to humans at a 1 to 1 level, these results suggest that gut bacteria can alter brain structures and affect behavior. Depression, anxiety disorders or autism, for example, could be partly related to a disturbed intestinal flora. Animal experiments suggest that these diseases can be alleviated by restoring the balance of a healthy intestinal flora.

The link to obesity and diabetes

Overweight is determined by the diet, the lifestyle, the genes and - as it looks - also by the genes of the personal microbiome. How fast or slow we use fat depends on the composition of our intestinal flora. Axenic mice, grown entirely without gut flora, have been given bacteria from lean or fat mice. And look - with the same food, the mice have become either slim or obese according to who their donor was. This is probably related to the different digestive efficiency. In addition, the intestinal flora affects the feeling of satiety. And there could be much more to it, because even the risk of diseases such as diabetes, fatty liver and arteriosclerosis can be transferred from one animal to another with the intestinal flora and reduced again with the right intestinal flora. The intestinal flora of humans also differs from person to person and is closely intertwined with body functions. It may sound strange, but it is very likely that these small creatures contribute much to our individual personality through their numbers and genetics. We are just at the beginning of this exciting research, but it is one of the most promising approaches to health and quality of life.